1. Field of the Invention
The present invention relates to a semiaromatic polyamide resin composition which exhibits excellent anti-creeping property under high temperature and high humidity conditions, causes less contamination to the metal mold (mold deposit) during the molding operation, and can make a molded parts easy to be ejected from the mold.
2. Description of the Prior Art
There have heretofore been proposed a variety of semiaromatic polyamides having shock resistance. For example, Japanese Unexamined Patent Publication (Kokai) No. 108855/1992 discloses a method of producing a polyamide composition comprising:
a semiaromatic polyamide having; PA1 a modified elastic copolymer. PA1 (A) a polyamide copolymer in which a main constituent component unit is a polyamide formed of a recurring unit of a dicarboxylic acid component unit and a diamine component unit, at least not less than 45 mol % of said dicarboxylic acid component unit being a terephthalic acid component unit, and said diamine component unit comprising a straight-chain alkylenediamine component unit having 4 to 18 carbon atoms and/or an alkylenediamine component unit having a side-chain alkyl group and 4 to 18 carbon atoms; PA1 (B) an aliphatic polyamide containing, as a constituent unit, at least the one selected from the group consisting of (i) a unit derived from a lactam having 12 carbon atoms, (ii) a unit derived from an aminocarboxylic acid having 12 carbon atoms and (iii) a unit derived from a dodecanoic diacid and a diamine; and PA1 (C) at least one kind of graft-modified product selected from the group consisting of a graft-modified ethylene/.alpha.-olefin copolymer, a graft-modified product of an aromatic vinyl compound/conjugated diene copolymer, and a graft-modified product of a hydrogenated product of the graft-modified aromatic vinyl compound/conjugated diene copolymer; PA1 1. the polyamide copolymer (A) has a melting point over a range of from 280 to 330.degree. C. as measured by DSC; PA1 2. the polyamide copolymer (A) contains an aromatic carboxylic acid unit other than the terephthalic acid and/or an aliphatic dicarboxylic acid unit having 4 to 20 carbon atoms in an amount of not larger than 55 mol % per the whole dicarboxylic acid units; PA1 3. the polyamide (B) has a flexural modulus of elasticity of not smaller than 1300 MPa as measured in the form of a test piece obtained by the injection molding in compliance with ASTM D 790; and PA1 4. the graft-modified product (C) has a density over a range of from 0.85 to 0.95 g/cm.sup.3.
(a) a dicarboxylic acid unit comprising 50 to 100 mol % of a terephthalic acid unit and 0 to 40 mol % of aromatic dicarboxylic acid other than terephthalic acid or a straight-chain aliphatic dicarboxylic acid unit having 6 to 18 carbon atoms; and PA2 (b) an alkylenediamine unit; and
It has also been known that the composition comprising such a semiaromatic polyamide and a modified elastic polymer, features excellent heat resistance and shock resistance (Japanese Unexamined Patent Publications (Kokai) Nos. 41318/1990 and 98152/1993).
Such polyamides are very excellent with respect to shock resistance, heat resistance, mechanical properties, and chemical and physical properties, but often precipitate a white powder in the metal mold when they are injection-molded repetitively by using a metal mold. When used for electronic equipment, furthermore, these polyamides fail to exhibit satisfactory anti-creeping property under high temperature and high humidity conditions, leaving room for improvement.
The present inventors have analyzed the powder and have discovered that the powder comprises unreacted monomer, low grade oligomer component and decomposed product of polymer. The unreacted monomer, low grade oligomer and decomposed product of polymer become a cause of problem, impairing the appearance and dimensional precision when the electronic parts are to be molded and, particularly, when fine parts are to be molded such as connectors. Besides, the white powder formed in the metal mold clogs the vent holes of the metal mold. Therefore, the molding operation must be interrupted to clean the metal mold.
The present inventors have previously proposed a semiaromatic polyamide resin composition comprising a particular polyamide copolymer and a modified ethylene/.alpha.-olefin copolymer (Japanese Patent Application No. 52273/1998). This resin composition effectively improves the above-mentioned problem, exhibits excellent mechanical strength such as rigidity, shock resistance and bending strength, exhibits excellent anti-creeping property, exhibits excellent chemical and physical properties such as shock resistance and heat resistance, causes little contamination to the metal mold (mold deposit) during the molding operation for a long time, little cause the vent in the metal mold to be clogged, and makes it possible to obtain precisely molded articles having excellent appearance, which are excellent advantages.
However, the previously proposed resin composition has a problem in that it requires a large force for being ejected from the metal mold after molded. When articles such as connectors are to be molded, for example, metal molds having complex structures are used, and the molded articles are poorly parted, still leaving much room for improvement.